It is the recommendation of the American Academy of Pediatrics that all children be breast-fed for at least the first six months of life [2], Despite this recommendation, the functional development of the mammary gland and the result of that development, milk secretion, have received relatively little attention over the past two decades. In this program project we seek to remedy this deficit by bringing together six well-qualified investigators with varying expertise to examine four critical aspects of the regulation and mechanism of milk secretion. In Project I we will examine a new hypothesis that links balanced glycolysis in the mammary gland both to lipid synthesis and cell survival. We hypothesize that changes in the activity/conformation of hexokinase regulated by the serine/threonine kinase Akt/PKB provide the crucial link between these two functions. We will test the hypothesis in genetically altered mice. In Project II, we will examine the molecular and cell biological basis of the formation of cytoplasmic lipid droplets (CLD) in the mammary alveolar cell, testing the hypothesis that these entities originate within specialized domains in the endoplasmic reticulum containing all the necessary synthetic machinery machine for their synthesis. In project III, we will scrutinize the mechanisms by which progesterone inhibits the initiation of milk secretion in late pregnancy examining both direct and indirect mechanisms and their localization in the mammary gland to progesterone receptor containing cells and other cells. Strains of genetically altered mice in which the LacZ has been targeted to the progesterone receptor coding region and green fluorescent protein to the b-casein coding region will be used to accomplish this aim. In Project IV we will initiate studies of the role of PKC* on cell proliferation and apoptosis in pregnancy, lactation and involution. T his serine/threonine kinase is an upstream regulatory factor in epithelial cell apoptosis and we will use it to elucidate the pathways through which mammary epithelial cell survival can be compromised by milk stasis or hormone withdrawal. These studies will form a foundation on which to base an understanding of why lactation does not always proceed optimally and in the long run should help us increase the human milk supply for infants, particularly preterm infants, for whom human breast milk is a priority.